There are no plans to discontinue providing compiled applications. While this practice started before flatpaks were as widely available and reliable, we still feel that the compiled packages represented the curated, quality software experience we want to provide. As brent points out, we can control the quality of an app we compile, but not a flatpak distributed by someone else.
Additionally, it would take a lot of work to convert Solus from a distro that provides repo packages + flatpak support to flatpaks as default. This would increase, not decrease the amount of work we do.
We also have no plans to officially support something like the AUR or a user based repository. This would also be contrary to the goal of having a curated repository of apps. Anyone who wants to package an app can and is encouraged to do so, and submit it for inclusion in the repo. If they are willing to maintain it, and we see it's a quality contribution, we are very like to accept it.
The only difference between a user packaged thing in a user repo and in the official repo is that the latter has additional quality checks. This is a good thing.